It is well known to employ an electromagnet as a transducer between electrical and mechanical portions of a camera shutter controller. In typical practice, the electromagent is energized and later de-energized with the point of time at which de-energization occurs being the determining factor as to exposure duration control.
In accordance with this typical practice, some mechanical element is for a time held fixed as a result of the magnetic attractive effects of the electromagnet. Upon de-energization of the electromagnet, the particular mechanical element is released so that it can move in response to spring biasing or the like. The ensuing movement brings about various results depending upon the particular type of camera involved. For example, in a camera having an objective shutter, the shutter blade is typically open while the electromagnet is energized and upon de-energization it closes in response to biasing force. In a camera having a focal plane shutter, the follower curtain of the shutter is released in response to de-energization of the electromagnet and it thereupon travels from its wound up position to its end position. Another example involves diaphragm blades which are held at a particular aperture according to particular photographing requirements.
The interval during which the electromagnet is maintained energized is a variable factor. For example, in connection with a shutter, this interval depends upon the appropriate exposure time. Accordingly, where a relatively long exposure time (e.g., in the order of two seconds) is appropriate, the typical practice involves energizing the electromagnet for a correspondingly long period. Consequently, considerable electrical power is consumed. This causes a problem with respect to draining the battery used in the camera. Usually, such a camera battery is a miniature one, owing to the severely limited space allotted thereto in the camera. This problem has created a substantial demand for an effective means for saving battery power consumption. From this viewpoint, disadvantages inhere in the electromagnetic mechanism adapted to be controlled through de-excitation in the manner described above. There has been proposed on arrangement such that the electromagnet is controlled through excitation with an impulse produced at a suitable time point, using a permanent magnet as the magnetic core. However, this arrangement also has been disadvantageous in that a magnetic time lag is involved in the releasing operation. That is, a relatively prolonged time lapse follows de-energization of the electromagnet before the moment at which the electromagnet presents a given magnetic force. The releasing operation itself is apt to be unstable inasmuch as the electromagnet should be electrically polarized in opposition to the polarity of the permanent magnet. Accordingly, the magnet assembly as a whole should be unexcited. Particularly when adapted for use with the camera shutter, this arrangement presents serious disadvantages in that it is difficult to maintain a desired accuracy in cases where relatively brief exposures are required.